nited States - NTRS - NASA

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May 8, 1984 - The microballoon is filled with heavy hydrogen cryo- ... ents of electromagnetic, acoustic or gas inertial origin, .... the inward swings attenuate with the expanding cross- the axis of said structure D and does not laterally dis-.

nited States


Dum et al.


[54] SONIC LEVITATION APPARATUS [75] Inventors: Stanley A. Dunn; Alan R. Pomplun; Elmer G.Paquette, all of Madison, Wis.; Edwin C. Ethridge; Jerry. L. Johnson, both of Huntsville, Ala.

[73] Assignee: The United States of America as represented by the Administrator of the National Aeronautics and Space Administration, Washington, D.C.

[21] [22] [513 1521

Appl. No.: 493,866 Filed:

May 12, 1983

Int. a.3..............................................

C03D 19/10

US. CY. ....................................... 65/14; 65/21.3; 65121.4; 65/160; 1371838; 36~106;42516 [58] Field of Search ................366/106, 127; 137/838; 65/21.3, 21.4, 142, 160;425/6 [561 References Cited U.S. PATENT DOCUMENTS

4,400,191 SA983 Miller et al.

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OTHER PUBLICATIONS NASA Tech. Briefs, vol. 5, #2, Summer 1980,p. 236, Controlling the Shape of Microballoons.

Primaly Examiner-Robert L. Lindsay, Jr. Attorney, Agent, or Firm-Leon D. Wofford, Jr.; John R. Manning; Joseph H. Beumer

VI ABSTRACT A sonic levitation apparatus (A) is disclosed which includes a sonic transducer (14) which generates acoustical energy responsive to the level of an electrical amplifier (16). A duct (B) communicates with an acoustical chamber (18) to deliver an oscillatory motion of air to a plenum section (C)which contains a collimated hole structure (D) having a plurality of parallel orifices (10). The collimated hole structure converts the motion of the air to a pulsed, unidirectional stream providing enough force to levitate a material specimen (S).

2,911,669 11/1959 Beckwith ......................... 65/21.3 X 4,313,745 2/1982 Kendall ................................ 65/21.4

20 Claims, 3 Drawing Figures



US. Patent

May 8, 1984

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19 1



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the collimation and other levitating properties of the issuing streams. The higher the aspect ratio the greater the persistence. ORIGIN OF THE INVENTION Due to the fact that the holes have been formed hereThe invention described herein was made in the per- 5 tofore by drilling, they have been of limited aspect ratio as well as being circular. formance of work under a NASA contract and is subA need also exists for apparatus for preparing solid ject to the provisions of Section 305 of the National particles of materials such as novel glasses under condiAeronautics and Space Act of 1958, Public Law 85-568 tions enabling a quick quench and avoiding contact (72 Stat. 435; 42 USC 2457). 10 with a container. BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION The invention relates to a levitation microfurnace apparatus for processing and shaping small bodies Accordingly, an important object of the present inwhere contact with foreign objects or supports could be vention is to provide apparatus for levitating a GMB or deleterious. In particular, the invention has application l5 other small object which is simple yet reliable and suffito the processing of minute glass microballoons or miciently' precise for levitating and processing a GMB in a crospheres. The microballoon is a thin wall glass struclow gravity environment. ture such as used in the processing fuel in laser fusion. Another important object of the present invention is The microballoon is filled with heavy hydrogen cryoto provide a simple method of fabricating high aspect genically condensed as a thin layer on the interior of the 2o ratio collimated hole structures (CMS)for producing walls. It is then bombarded with energy focused from a levitating flows of parallel, equispaced, equivelocity laser. The glass material then vaporizes and the hydrostreams of gas or liquids. gen contained therein is driven to the center by inertial Another important object of the present invention is reaction and compressed to a very dense and very hot to provide without the use of valves or other moving plasma material resulting in fusion of the hydrogen. 25 parts, a simple means of converting sonic energy into Glass microballoons (GMBs) which are used to conpulsed unidirectional flows of gases or other fluids tain the fuel must be precisely spherical and have uniwhich may be suitable for levitation of GMBs or other form wall thickness. Those obtainable commercially are small bodies. only rarely of the required degree of perfection. Sorting Yet another important object ofthe present invention them out from the accompanying imperfect GMBs is a 3o is to provide a sonic powered levitation device wherein major task. levitation is achieved by aerodynamic lift imparted to a It is thought that the imperfect GMBs might be small body specimen from a pulsating gaseous flow brought to any degree of geometric perfection by reproduced by passage of sonic energy through the gas melting, reprocessing and recooling, all the time maintaining them in a levitated state, out of contact with 35 within a CHS, which eliminates the need for moving valve parts. solid or liquid objects. Alternatively, this containerless Still another important object of the present inventype of processing might be applied to the initial formation is to provide a sonic levitator which may be used tion of GMBs from porous glass frit or other suitable along the axes of an orthogonal trimid coordinate sysprecursor materials, as well as to their reprocessing. Accordingly, apparatus for levitating the microbal- 40 tem to levitate a body of material in a variable low gravity environment. loons in a microfurnace so that their formation may be It has been found according to the present invention, accurately controlled to provide a more perfectly and that the sonic output of a sound generator ducted into a uniformly formed balloon is a problem to which considcollimated hole structure will prau&%e,above the free erable attention need be given. In order to form GMBs of large diameters such as up 45 end, sufficient net air flow in one direction to levitate a GMB or other small body. The CHS9 comprising an to one centimeter, it is necessary to process them in a array of parallel passages, is carried adjacent to the end low or zero gravity condition such as in space. While of a tubular duct which is connected to a chamber of the apparatus is well known for levitating a specimen of sonic energy generator. The sonic energy generator is material in a gravitational field by opposed field gradients of electromagnetic, acoustic or gas inertial origin, 50 driven by a sinusoidal or other periodic pressure source. The CHS behaves as a rectifier of the oscillatory sound these apparatus are not entirely suitable for levitating a energy, converting it into a pulsating gas flow in one microsphere in a low gravity environment, where acdirection only which is useful in levitation. Between the celerations are typically variable, not only with respect sound generator and the free or upper surface of the to magnitude but direction as well. When positioning and levitation of a GMB in an orthogonal triaxial coor- 55 CHS the gas undergoes no net movement, only the oscillatory motion typical of sound transmission. Above dinate system is necessary such as in processing the the free surface of the CHS, the outward and inward GMB in space, the problem of rapid and accurate conswings of each sound vibration become differentiated trol of restoring forces to neutralize unwanted extranewith respect to direction. The inward swings are charous accelerations becomes particularly acute. One well known method of levitation involves a colli- 60 acterized as omnidirectional, moving toward the CHS openings more or less symmetrically from all available mated flow of a number of equispaced equivelocity direction of the 27r steradians above the CHS surface. streams of gas or liquid impinging upon a GMB or other The outward swings, by contrast, are unidirectional and small body in such a way as to counter and neutralize aligned with the CHS passages. The oscillatory sonic the net force vector tending to displace the body from a preferred position. The device whence these streams 65 character of the gas at the CHS surface gradually gives way to pulsed unidirectional flow with height, the tranissue is commonly called a collimated hole structure sition being virtually complete at an elevation about a (CHS). The depth of the CHS holes in relation to their plenum diameter above the CHIS surface. The transition diameter, their aspect ratio, influences the persistence of SONIC LEVITATION APPARATUS


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is due to the fact that the outward swings being aligned D from all angles of bearing and azimuth. This ingested and of constant cross-section are of constant flux denair or fluid when expelled during the outward stroke, sity with height above the CHS while the flux density of however, is carried by its momentum in alignment with the inward swings attenuate with the expanding crossthe axis of said structure D and does not laterally dissection characteristic of their radial flow pattern. In 5 perse, thus creating a unidirectional pulsating jet suitessence, during each sound vibration the sonic pump able for levitation. As illustrated, the collimated structure D includes a brings in air or other fluid from all directions surrounding the mouth of the CHS and ejects it in one direction plurality of parallel passages 10 formed in a plenum 12 only. which is carried adjacent the free end of the duct means It has also been found according to the present inven- 10 B. As can best be seen in FIG. 2, the collimated passages tion that the cross-section of the holes in a CHS need are comprised of the interstices between and among a not be circular and, consequently, that CHSs of any four by four matrix of uniform diameter rods snugly aspect ratio desired may be made consisting of the interfitted within the plenum in rectilinear array. There are stices in a tight, regular bundle of equal length uniform nine full size interstitial passages of quatrefoil cross-secdiameter wires. The bundling may be either a hexagonal 15 tion located centrally. At the boundaries with the pleclose packed or a rectilinear array. num there are twelve half size and four quarter size The sonic generator may be driven by any convenfurther passages all with trefoil cross-sections. The tretional amplifier. Levitation is initiated by simply raising foils contribute little to the levitating flow because of the power of the amplifier with the GMB or microtheir smaller effective diameters. Circular cross-section snhere resting on the surface of the collimated hole 20 collimated passages are well known and may also be structure. Asthe power is increased, the microsphere used, of course. first hops around in response to the oscillatory flow Sound generator A may include a conventional sonic character at the surface. Eventually, it will hop high transducer device 14 which may be any suitable audio enough to attain a level where the unidirectional flow is loudspeaker for converting electrical energy into sound dominant whereupon it will become stably levitated. 25 energy. A power source is illustrated at 16 for driving the sonic transducer 14 which may be any suitable elecBRIEF DESCRIPTION O F THE DRAWINGS trical amplifier. By varying the level of the amplifier 16, The construction designed to carry out the invention the electrical energy driving the loudspeaker 84 may be will be hereinafter described, together with other feavaried to vary the sonic energy and the flow momentum tures thereof. 30 of the pulsed levitational stream as required. The invention will be more readily understood from The loudspeaker device 14 includes an acoustical a reading of the following specification and by referchamber 18 in which a sound energy transporting meence to the accompanying drawings forming a part dium or fluid such as air is contained. thereof, wherein an example of the invention is shown Closure means for sealing the acoustical chamber and wherein: 35 includes a flat plate 19 sealed to the loudspeaker at its FIG. 1 is a schematic view illustrating a sonic pump edges 20 and perforated at 22 to provide communicatlevitator constructed according to the present invening into the acoustical chamber 18. tion; The cross-section of said member 24 is square as a matter of convenience although it could be circular, FIG. 2 is an enlarged top plan view of the collimated hole structure for levitating a microsphere as illustrated $0 hexagonal or other compact closed shape offering miniin FIG. 1;and mal resistance to flow. The upper or free end of member FIG. 3 is a schematic view of the axial arrangement 24 serves as the plenum housing the interstitial colliof six acoustical levitator devices constructed in accormated hole structure, its square cross-section nicely dance with the present invention as arranged along the accommodating the rectilinear array of interstitial formaxes of a triaxial orthogonal coordinate system for levi- 45 ing rods. Any slack between the rod matrix and the interior of the plenum is taken up by appropriately sized tating a microsphere in a stable levitating position under shim stock (not shown in FIG. 2) to achieve a snug fit. low gravity conditions. Alternatively, instead of tubing, the plenum may be DESCRIPTION O F A PREFERRED formed between mating blocks, a rectangular groove EMBODIMENT 50 being machined in one of them to just accommodate the The drawing illustrates a sonic pump levitation apparods and provide a snug fit when the blocks are bolted together. The matrix may also be made up of a bundle ratus for levitating a microsphere which includes a sonic generator, designated generally as A, having an or wires of fibers. acoustical chamber in which a sound energy transportSound generation by the loudspeaker 14 results in a ing fluid is contained. A closure means seals the cham- 55 corresponding sinuously reversing flow in the duct ber from the outside environment and includes a medial means B. At the mouth of the collimated hole structure opening which communicates with a tubular duct D are two entirely different flow patterns for the fluxes means B which terminates in a free end. Means for in and out of the orifices 10 of the collimated hole strucdriving the sound generator and producing a periodic ture. The influx pattern is nearly isotropic and the efpressure source is provided by an electrical power 60 flux, although pulsating, is in one direction only and in source. A plenum means C is carried adjacent the free other respects similar to the desired collimated flow resulting from a constant pressure supply of gas through end of the tubular duct and includes an interstitial collithe collimated hole structure. mated hole structure D within plenum C by means of The dichotomous flow pattern stems from the fact which sonic energy impressed upon the air or fluid within said structure D is converted at and above the 65 that the influx is dictated by pressure gradient and the free end into a unidirectional pulsed stream of air suitefflux by momentum of the gas. The collimated hole able for levitation. The inward stroke of each sound structure orifices behave as a gas sink during the influx. cycle draws air or fluid into the mouth of said structure Since no momentum bias is involved, a more or less

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their length to diameter, and is preferably in the range isotropic system of isobars and pressure gradients develops, directing the flow accordingly. Inherent in the of 5:l to 501. efflux, however, is the momentum engendered in the air Levitation was initiated by resting the glass microduring its flow through the collimated hole structure D. sphere on the surface of the collimated hole structure These momentum vectors are not soon dissipated and 5 and raising the level of the power transmitted by amplithey dominate for some distance above the collimated fier 16.As the power was increased, the glass microhole structure, thereby maintaining alignment of the sphere first bobbed around the surface of the collimated flow with the collimated hole structure axis, and prehole structure and thep leaped up to around a millimeter cluding radial diversion analogous to the radial confrom the surface and locked into a stable levitation 10 position. Once levitated, the glass microsphere could be verging pattern of the influx. The inertia of the loudspeaker cone is such that the raised and lowered over a range of several millimeters response times are easily obtainable with an off-theby adjusting the power fed to the loudspeaker 14.Levishelf loudspeaker item of modest cost and high reliabiltation was accomplished utilizing the four inch ten watt ity. Furthermore, the output of the air stream is a monoloudspeaker operated in a range of approximately 750 tonic and sensitive function of the incoming electrical 15 hertz. energy or signal to the loudspeaker. As illustrated in FIG. 3, six sonic levitation apparatus While the sonic pump levitation apparatus resembles A are illustrated with the members of each of three pairs some fluidic devices in its switching of gas flow patbeing arranged in opposition along an axis of a triaxial terns, this is accomplished without any reliance upon orthogonal coordinance system. In this manner, the conventional valving mechanism or vanes or, indeed 20 microsphere or microballoon may be levitated in a any moving part except the vibrating loudspeaker cone stable position when undergoing processing in low The apparatus provides a simp1e and unique gravity environments such as in space. In this case, a for converting an gas flow into a conventional computer or microprocessor 30 may be pulsating direct current flow, to use the electrical idiom. utilized in conjunction with a video scanThis pulsating DC flow is capable of levitating suitably 25 ner 32 of the specimen s to maintain the positioning of sized bodies such as glass microballoons and solid mithe microsphere or microballoon through feedback crospheres. control of the energy level of amplifier 16 and loudThe intensity of the acoustical generator, and hence speaker 14 of each sonic pump device. the height of levitation is easily and rapidly controlled by adjustment of the power to the loud- 3o Deviations in the levitation position of the microsphere s can be detected by the video Scanner and input speaker. Response time is of the order of the reciprocal to the computer. The computer then generates an decof the upper frequency limit of the speaker. The glass trical signal from the feedback loop which corrects the microba~loonsare of the order of a millimeter in diamelevitational position by increasing or decreasing the ter. Under these conditions, power levels of about a quarter of a watt produce stable levitation. Except in 35 power fed to a loudspeaker and thus correcting the gas the region immediately above the collimated hole strutpulses from the levitational apparatus as required. Since the gas pulse must have very rapid UP and down times, ture plenum, stability is comparable to that obtained with the steady flow of levitation gas. This region of on the order of a milisecond, apparatus of the present instability, which extends for about a diameter of the invention is particularly advantageous since there are plenum above the surface of the collimated hole strut- 40 no moving Parts. Valve systems have very high inertia ture, coincides with the cross-over of the influx and and not very rapid response times. In accordance with the present invention, the apparatus disclosed berein has efflux flow patterns. very rapid response times and is very readily usable in The high aspect ratio of the Passages of the callimated hole structure and the relatively long distance Such an automatic system. between the collimated hole structure plenum to the 45 While a Preferred embodiment of the invention has loudspeaker thermally isolate the levitation flow from been described using specific terms, such description is for illustrative pvrposes only, and it is to be understood all elements of the apparatus in back of the plenum. Thermally sensitive components such as the loudthat changes and variations may be made without despeaker thus may be safely incorporated with high ternparting from the Spirit OF Scope of the following claims. 50 What is claimed is: perature levitating conditions. 1. Apparatus for levitating a material specimen comEXAMPLE prising: In one embodiment, a four-inch ten watt loudspeaker a duct having an interior adapted to be filled with gas; was utilized to generate enough air flow in one direca collimated passage means disposed within and at an end of said duct, said collimated passage means tion to levitate a solid six hundred micron glass micro- 55 sphere. The face of the speaker was covered with a flat including an array of parallel passageways communicating with the interior of said duct with the steel plate 4 of an inch thick and a duct B was made utilizing a 4 inch square tubing approximately 2.75 surrounding atmQsphere; and inches long. The collimated hole structure D was cona sound generator means for imparting oscillatory motion to the gas within said duct so as to provide tained in a plenum means 12 and was comprised of the 60 levitating force irl. the form of pulsed, unidirecinterstices 10 in a square array of 16 equal lengths, equal diameter rods held in place by the clamping action of tional motion of gas axially beyond the end of said suitably sized shims (not shown) inserted along the collimated passage means. 2. The apparatus of claim 1 including an acoustical adjacent sides of plenum means 12. The length of the interstitial passages is 0.5 inches. The rod diameter was 65 chamber in communication with the interior of said duct. 0.025 inches, hence the passage diameter varied from a 3. The apparatus of ulaim 2 wherein said duct is dismaximum of 0.025 to a minimum of 0.010 inches. The posed vertically. aspect ratio of the passages is defined as the ratio of

4,447,25 1 4. The apparatus of claim 3 wherein said acoustical

chamber is joined to the lower end of said duct and sealed from the outside environment. 5. The apparatus of claim 4 wherein said sound generator means includes a device for converting electrical energy into acoustical energy. including a 6. The apparatus of claim power source of electrical energy connected to said sound generator means for controllably varying said acoustical energy and the levitational forces produced thereby. 7*The of claim a plurality of solid rod, wires or fibers of circular cross-section disposed vertically in a bundle within a Plenum region forming the upper end of Said duct, the open Spaces betweeri the said rods, wires or fibers providing an array of parallel passageways. 8. The apparatus of claim 6 wherein said duct is a tube of generally rectangular cross-section. 9. The apparatus of claim 8 wherein the ratio of length to diameter of said rods is in the range of 5:l to 50:1. 10. The apparatus of claim 9 wherein the length of said rods is about 0.5 inch and their diameter 0.025 inch. 11. The apparatus of claim 6 wherein said acoustical chamber is contained in an upwardly extending, conical-shaped speaker having its upper periphery sealed to a flat plate. 12,The apparatus of claim 11 wherein said plate is penetrated by a central passageway axially above the center of said speaker, the said plate being sealed to the lower end of said duct around the periphery Of said plate passageway. ’ 13- An apparatus for providing a pulsed, unidirectional gas flow comprising: a tubular duct adapted to be filled with gas; a collimated passageway structure disposed within and at an end of said duct, said structure having an array of parallel passageways communicating the interior of said duct with the surrounding environment;














a sound generator means for imparting oscillatory motion to the gas within said duct, thereby providing a pattern of pulsed, unidirectional gas flow at a zone located beyond the outer end of said passageway structure. 14. The apparatus of claim 13 wherein said sound generator means comprises a conical speaker disposed in axial with said duct‘ 15. The apparatus of claim 14 including a flat plate sealed to the extended end of said speaker and penetrated by a passageway communicating the acoustical chamber contained therein with the inerior of said duct. 16.The apparatus of claim 15 wherein said collimated passageway structure comprises a plurality of rods of circular cross-section and uniform diameter disposed in axial alignment so as to provide axially extending open spaces therebetween. 17.Apparatus for levitating a material specimen in a low or variable-gravity environment comprising: a plurality of tubular ducts arranged in opposed pairs in a triaxial orthogonal coordinance system, each of said ducts having an interior adapted to be filled with gas and containing at one end a collimated passage means including an array of parallel passageways communicating with the interior of the duct with the surrounding atmosphere and at its other end a sound generator means for imparting oscillatory motion to the gas within the duct so as to provide levitating force in the form of pulsed unidirectional motion of gas axially beyond said collimated passage means; and means for variably supplying energy to said sound generator means. 18. The apparatus of claim 17 including means for sensing the position of a specimen levitated therein and controllably adjusting the energy supplied to said sound generator means so as to maintain said specimen at a predetermined location. 19,The apparatus of claim 18 wherein said sound generator means is a loudspeaker. 20. The apparatus of claim 19 wherein said sensing means is a video scanner.